Interesting. It sounds like the study is saying it's cheaper if external costs like climate change are factored in, but I wonder how soon in the future it will be cheaper in absolute terms? Some places where electricity is very expensive, like Hawaii, have already reached grid parity for solar. Here's a detailed explanation of how soon parity is coming in other U.S. locations: http://grist.org/article/solar-costs-and-grid-prices-on-a-collision-course/